The Cameroonian ace only left the Gunners to join Barcelona in 2012, but has endured a thoroughly underwhelming spell at the Camp Nou.
Limited appearances and below par displays when called on have seen the enforcer deemed surplus to requirements, with the Catalans ready to sell.
Even though he has flopped in Spain, Chelsea and United are keen to bring him back to the Premier League.
Barca are thought to be demanding close to £20m, yet both English sides are unlikely to stump up such a sum for a player who made only 39 outings in two years.
The 26-year-old is also ready to make a comeback, with his spell at his current club having been a disappointment.
Song has been away with his nation at the World Cup recently, where he received a red card in the third of three losses in Group A.